Environmental health: photochemical smog: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Environmental health: photochemical smog

Sample item

A city with heavy vehicular traffic and strong sunshine, but little coal burning, has summer haze with eye irritation and high ground-level ozone. Which pollutants react in sunlight to produce this?

AChlorofluorocarbons and halonsBCarbon monoxide and carbon dioxideCNitrogen oxides and hydrocarbonsDSulphur dioxide and particulate soot

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Nitrogen oxides and hydrocarbons

Photochemical smog forms when sunlight acts on nitrogen oxides and hydrocarbons from vehicle exhaust, producing ozone and peroxyacetyl nitrate that irritate the eyes and respiratory tract. Classical London-type smog, in contrast, results from coal smoke with sulphur dioxide in cold, humid weather.

Option by option

A. Chlorofluorocarbons and halons
Chlorofluorocarbons and halons deplete stratospheric ozone and do not form ground-level smog.
B. Carbon monoxide and carbon dioxide
Carbon monoxide and carbon dioxide are not the reactants that produce ground-level ozone haze.
C. Nitrogen oxides and hydrocarbons (correct)
Correct. Sunlight drives reactions of nitrogen oxides and hydrocarbons to form ozone and other oxidants.
D. Sulphur dioxide and particulate soot
Sulphur dioxide with soot characterises the older coal-smoke smog of cold and humid weather.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is C, Nitrogen oxides and hydrocarbons. Photochemical smog forms when sunlight acts on nitrogen oxides and hydrocarbons from vehicle exhaust, producing ozone and peroxyacetyl nitrate that irritate the eyes and respiratory tract.

Why is "Chlorofluorocarbons and halons" not the answer?

Chlorofluorocarbons and halons deplete stratospheric ozone and do not form ground-level smog.

Why is "Carbon monoxide and carbon dioxide" not the answer?

Carbon monoxide and carbon dioxide are not the reactants that produce ground-level ozone haze.

Why is "Sulphur dioxide and particulate soot" not the answer?

Sulphur dioxide with soot characterises the older coal-smoke smog of cold and humid weather.

What concept does this question test?

It tests Environmental health: photochemical smog in PSM. Classical London-type smog, in contrast, results from coal smoke with sulphur dioxide in cold, humid weather.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Environmental health: photochemical smog?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.